> -----Original Message-----
> From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
> Sent: Friday, February 08, 2008 3:20 PM
> To: Langsdorf, Mark; xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] dom0 and apicid not equal to cpuid
> On 8/2/08 21:05, "Langsdorf, Mark" <mark.langsdorf@xxxxxxx> wrote:
> > Some AMD processor systems assign the boot processor
> > (cpu 0) to apicid 4. Standard Linux handles this
> > cleanly by keeping track of the correspondences amongst
> > cpu id, apic id, and acpi id. dom0 Xen does not have
> > the code to do that, and AMD is seeing some strange
> > behavior on our 4 socket quad-core systems.
> > Specifically, when we try to get ACPI information for
> > cpu 0, the correspondences break down and the request
> > fails.
> > I know some of the code needs to be added to mpparse-xen.c,
> > but it looks like the relevant code was #ifdef'd out in
> > the first place. Does anyone know why the code to match
> > cpuids to apicids was removed and what would need to be
> > done to restore it?
> Can you point out the specific troubling code in our Linux
> tree (e.g., the specific #if0'ed code, and also the place
> where the kernel ultimately gets confused and the request fails)?
Sure. in arch/x86_64/kernel/mpparse-xen.c,
there is no code in mp_register_lapic_address(), so dom0 has no
idea who the boot CPU is. Later, when mp_register_lapic() is
called, it still doesn't have this information, so it can't
pass this information to MP_processor_info(). MP_processor_info()
doesn't get the cpuid to apicid information from the previous
functions, so it sets the cpu_to_apicidp table using some other
method such that apicid is assumed to be cpuid. However, acpiid
is not the same as apicid, so later when drivers/acpi/processor_core.c
tries to recover _PSS objects, it can't always get the _PSS
objects because it starts searching at cpu id 4 (instead of 0)
and fails when looking for cpu id 16+ (on a system with 16
It appears that the call to GET_APIC_ID() in
mp_register_lapic_address() isn't legal for dom0, but the failure
to make that call results in an incorrect cpu_to_apicid table
and that means the acpiid_to_apicid table is also wrong.
Operating System Research Center
Xen-devel mailing list